Because of legal requirements, closing parts of a vehicle able to be moved by a direct current motor, for example sliding roofs or window panes, are equipped with an anti-trap mechanism which operates in accordance with a predetermined algorithm.
A known anti-trap algorithm is based on a comparison between a closing force curve calculated using Hall sensor pulses or using a motor current measurement and a reference force curve. The reference force curve is generally determined during the production of the respective vehicle by calibration during a closing process and is stored in a memory of the vehicle.
During this calibration the reference force curve is determined in the form of a friction force-lifting path diagram which exactly describes the respective mechanical system. This coverage accuracy is of great importance since any possible deviations between the reference force curve and the actual circumstances of the respective existing mechanical system lead to trap forces of different sizes. Variations of this type are undesired since the trap forces are restricted on the one hand by legal requirements, but on the other hand should be as high as possible to give the system sufficient robustness in relation to undesired motor stop or reversing processes.
An actuating drive for moving remotely-actuated closing parts in motor vehicles over a lifting path and with a definable anti-trap force when the closing part encounters an obstacle is known from DE 196 33 941 C2. This known actuator has a control dependency of the respective drive force of the closing part in accordance with a previously recorded operational friction force-lifting path diagram and with a friction force increased by the permissible closing force in each case. The said friction force-lifting path diagram is recorded during the production of the motor vehicle by the drive force which is detected during a closing process of the closing part as a function of the respective lifting path position in a diagram and stored in a memory device being calculated from the motor current or the motor speed and the motor voltage. Furthermore there is provision for an updating of the friction force-lifting path diagram such that systematic differences caused by ageing, contamination etc. can be taken into account.